Terminal pin resistor assembly for electric heaters



1959 L. D. DRUGMAND ET AL 2,899,666

TERMINAL PIN RESISTOR ASSEMBLY FOR ELECTRIC HEATERS Filed May a. 1957 2Sheets-Sheet 1 INVENTOR5 Lester D. Drugrnam y Jnseph TTl flrlly 1959 L;D. DRUGMAND ETAL Q 2,899,666

TERMINAL PIN RESISTOR ASSEMBLY FOR ELECTRIC HEATERS Filed May 8, 1957 2Sheets-Sheet 2 III Fig. 7

IN V EN TORS Easter D. Drvgmand By Joseph 'm firlly Htiorney TERMINALPIN RESISTOR ASSEMBLY FOR ELECTRIC HEATERS Lester D. Drugmand and.Joseph McOrily, Pittsburgh, Pa., assignors to Edwin L. Wiegand Qompany,Pitts burgh, Pa.

Application May 8, 1957, Serial No. 657,827

7 Claims. (Cl. 338-329) The present invention relates to electricheaters, more particularly to improved methods of making electricresistance heaters and to the improved heaters made thereby, and theprincipal object of our invention is to provide new and improved methodsand articles of such character.

In the manufacture of electric resistance heaters, a long standingproblem has been that of making suitable electrical connections to theresistor wire which becomes heated when current is passed therethrough.This problem becomes more and more acute as finer and more delicateresistor wires are employed and the need for a satisfactory, low costconnection, becomes even greater as heater production mounts since evena small percentage of rejects or a small saving in cost per unit amountsto large sums.

The present invention is particularly adapted although not necessarilylimited for use in manufacturing tubular metallic sheathed electricresistance heaters of the type wherein a coiled resistor is embedded incompacted, electric insulating, heat conductive material enclosed in atubular metallic sheath from whose one end a terminal pin protrudes. Theterminal pin extends into the sheath and is electrically connected withthe resistor and the protruding portion of the terminal pin is adaptedtobe connected to a source of electric current. Normally, a terminal pinis connected to each end of the coiled resistor member and each terminalpin protrudes from a respective end of the enclosing sheath; however,only one end of the resistor and its terminal pin will be disclosedherein since the arrangement at both ends is the same.

In the manufacture of certain types of heating elements, there existsnot only the necessity of obtaining a good electrical connection betweenthe terminal pin and the resistor but also the necessity of providing ahigh mechanical strength connection therebetween. This latter attendsbecause certain processes require that the resistor be tensioned bypulling the terminal pins at respective ends of the resistor in adirection away from each other. It has heretofore been proposed that theterminal. pin be welded to the resistor to provide a permanentconnection which possesses both high mechanical strength and lowelectrical resistance; however, in the past, insurmountable difficultiesstood in the path of a practical. application: of this obvious expedientto high production operations. Because of the small size of the resistorwires and because of the materials involved in the resistor wire and theterminal pin, it is necessary to precisely control both the pressureexerted by the welding electrode and the welding. current in order toobtain a satisfactory weld. Variations in one direction of either thepressure or the welding current may cause the resistor wire to becrushed or burnt so badly that the weld will have little strength. Onthe other hand, variations in the opposite direction may resultin theresistor merely being stuck to the pin with a resulting poor connection.While it has been possible to obtain United States "aten-t @fiice2,899,666 Patented Aug. 11, 1959 satisfactory welds under. lowproduction, laboratory type conditions, low cost, high production hasnot heretofore been possible without prohibitive losses in rejects.

The present invention provides a terminal pin-resistor assembly which isboth inexpensive and highly efiicient in producing perfect welds evenunder high production conditions where it is virtually impossible tomaintain the heretofore necessary ideal balancebetween welding pressureand welding current. Moreover, the present invention greatly reduces thenumber of difierent terminal pins required to accommodate coiledresistors of various sizes since one terminal pin may be used withequal'facility with a relatively widerange of resistor sizes. These andother advantages will readily become apparent from a study of thefollowing description and from the drawings appended hereto.

In the drawings accompanying this specification and forming a part ofthis application there is shown, for

purpose of illustration, embodiments which the invention mayassume, andin these drawings:

Figure 1 is a fragmentary elevational view of an assembly provided by apreferred embodiment of the present invention,

Figure 2 is a view similar to Figure 1 but'considerably enlargedandpartly in section to illustrate the interior construction,

Figure 3 is a view similar to Figure 2 but prior to the weldingoperation,

Figure 4 is a view similar to Figure 2 but showing the manner in whichthe weld is produced,

Figures 5 and 6'are views similar to Figure 3 but illustrating how thesameterminal'pin is used with coiled resistors both larger and smallerthan that shown in Figures 1' through 4; and

Figure 7 is a view similar to Figure 3 but of another embodiment oftheinvention.

Figures 1 and'2 illustrate a terminal pin 10 to which the coiled end ofa resistor 11' is secured to provide for electrical continuitytherebetween. Although it forms no partof the present invention, theresistor 11 with a terminal pin 10 at each end is usually, although notnecessarily; enclosed in a tubular metallic sheath withrespectivepinsprotruding from respective ends thereof, and thesheathfilled with powdered refractory material. which is" subsequentlycompacted by reducing the transverse sizeof'the sheath. The protrudingportion of'eachterminal'pin thereafter forms a rigidmemher to which" theusual electrical connections may be made.

The present invention is concerned with the manner in which the resistoris connected to the terminal pin and in the embodiment: shown in-Figures1 through 4, it will be noted that the resistor-engaging end of theterminal pin is disposed within the coiled end of the resistor and theendmost turns 13 of the latter are welded at 14' thereto (seeFigure 2).

In assembling the'terminal pin with the resistor, the tapered end oftheformer is inserted as far as it will go into the coiled end of thelatter as seen in Figure 3. Note that the taper of the pin assists itsentry into the resistor. The terminal pin is then engaged with theelectrode 15 of a suitable Welder (Figure 4) and another electrode 16thereof is then employed to clamp the endmost turns of the resistoragainst the adjoining surface'of the terminal pin. Current will then becaused to flow between respective welding electrodes 15, 16 to eifectthe weld. It' is to'be noted thatthe working face 17 of electrode 16- ispreferably parallel with the axis of the terminalpinfor a purpose toappear.

Referring particularly to Figures 2 and'4, it will be seen that theendmost turns'13- of the resistor end are secured to the pin by means ofa graduated weld. Note that the endmost turn of the resistor has beensecured to the pin with a considerable degree of fusion, the next turninwardlythereof with somewhat less fusion, and succeeding turns withprogressively less fusion. A graduated weld of this type-is highlyadvantageous as compared with welds not so graduated.

Prior art welds, as previously pointed out, were not satisfactorybecauseof the difliculty of maintaining the optimum degree of fusion betweenthe resistor and the terminal pin. By employing a graduated weld,however, the problem of optimum fusion is quite simply solved. Forexample, assume that the endmost turn of the re sistor were fused socompletely that it was practically burnt away. If this were the onlyturn welded or if all turns were so welded, a weld of little mechanicalstrength would result since the resistor wire would break under arelatively light stress at the place where it is welded to the pin.However, with the weld graduated inwardly from a point of maximum fusionat an endmost turn, successive turns will be welded with progressivelyless fusion. While it is true that some of the innermost turns engagedby the welding electrode will be barely fused to the terminal pin, oneor more turns intermediate such barely fused turns and the overly fusedendmost turn will have the optimum degree of fusion. Accordingly, evenif some of the innermost turns come loose from the terminal pin understress because of their lack of fusion, successive turns outwardlythereof having a progressively greater degree of fusion will remainsecurely welded to the terminal pin.

In order to produce consistently good welds even under high production,it is only necessary to make certain that there is at least optimumfusion between the terminal pin and the endmost turn of the coiledresisor Welded thereto. Indeed. a certain degree of more than optimumfusion is desirable at this place since this will insure that at leastone turn will be subiect to optimum fusion even though the weld variesas a result of electrode wear, variations in resistor wire hardness,line voltage variations, or any of the many other factors which have aneffect on resistance welding.

In order to obtain the raduated weld hereinabnve described, it ispresentlv preferred to exert a graduated clamping pressure uponsuccessive turns of the c iled resistor during the welding operation. Asherein. disclosed. the endmost turn of the resistor will be subiected tomaximum clamping pressure while successive turns inwardly thereof willbe sub ected to progressively less pressure. This is accomplished bydisposing the respective surfaces between which the resistor is clamped(i.e.. the terminal pin portion within the coil resistor and the workingface 17 of electrode 16) at an angle to each other.

In the embodiment thus far disclosed, this angular relationshi isprovided by v rtue of the fact that the terminal pin end is taperedwhile working face 17 of electrode 16 is parallel with the axis of theterminal pin. It is to be understood, however, the aforesaid angularrelationship may be increased or decreased to obtain the desiredgraduated weld b chan ing the plane of working face 17 of electrode 16by either tilting this electrode or by forming surface 17 at a differentangle to the axis of the electrode.

The taper of the terminal pin, in addition to providing the abovedescribed angularity which makes possible the graduated Weld, alsoperforms another extremely desirable function. This taper permits thesame terminal pin to be used with resistors having different insidediameters and therefore greatly reduces the number of diiferent terminalpins which need be stocked for various heaters.

In the usual construction, a terminal pin is proportioned to fit withinbut 'one size resistor such as resistor 11 and in the event resistors'of other sizes are to be used, a

different terminal pin must be employed. However, by

using the tapered terminal pin herein disclosed, the same pin may beused witha coiled resistor 11a having a much larger inside diameter(Figure 5) or with a resistor 11b (Figure 6) having a much smallerinside diameter. All that need be done is to insert the tapered end ofthe pin into the resistor until they are in close engagement and thenproceed with the welding operation. Note that the pin enters a greaterdistance into resistor "11a before engagement therebetween occurs whilethe pin enters a lesser distance into resistor 11b before suchengagement.

In the embodiment shown in Figure 7, the end of the terminal pin lid isprovided with stepped diameter portions 18, 19 and 20 each proportionedto closely fit within a different inside diameter coiled resistor. Pinportion 19 is adapted to fit within resistor 111 which may be the samesize as resistor 11. Portion 1% is adapted to fit within a resistor ofthe same size as resistor 11a while portion 20 is adapted to fit withina resistor of the same size as resistor 11]). While three portions 18,19 and 2% have been shown, it is to be understood that a greater orlesser number of portions may be formed on the pin to accommodate it foruse with a greater or lesser number of differently sized resistors.

In the embodiment shown in Figure 7, the heretofore graduated weld maybe obtained by tilting the axis of the welding electrode which engagesthe coiled resistor so as to effect the desired angularity between therespective surfaces of the welding electrode and the terminal pinbetween which the resistor is clamped during the welding operation or byotherwise disposing the working face of the electrode at an angle withrespect to that surface of the pin against which the resistor isclamped.

In view of the foregoing it will be apparent to those skilled in the artthat we have accomplished at least the principal object of our inventionand it will also be apparent to those skilled in the art that theembodiments herein described may be variously changed and modified,without departing from the spirit of the invention, and that theinvention is capable of 'uses and has advantages not herein specificallydescribed, hence it will be appreciated that the herein disclosedembodiments are illustrative only, and that our invention is not limitedthereto.

We claim:

1. An electric heater, comprising a helically coiled electrical resistorand a terminal conductor pin having an end thereof fitting within saidresistor and Welded to a plurality of adjacent convolutions thereof, thedegree of fusion of the weld progressively decreasing from convolutionto convolution in a direction inwardly of said resistor, wherebysuccessive resistor convolutions are secured to said pin by means of agraduated welded connection providing progressively increasingmechanical strength in a direction inwardly of said resistor and minimumelectrical resistance at the outer end thereof.

2. In an electric heater, the combination comprising a resistor memberhaving a coiled end providing a plurality of turns in side by siderelation and a terminal conductor pin secured to said resistor memberend to provide electrical continuity therebetween, one end of saidterminal conductor pin being tapered for close fitting engagement withinsaid coiled resistor conductor end and the latter being welded to thatterminal conductor pin portion which is in close fitting engagementtherewith by clamping said coiled resistor member end between saidterminal conductor pin and a welding electrode and passing weldingcurrent through said resistor member end and said terminal conductorpin, one of the endmost turns of said coiled resistor member end engagedby the welding electrode being subject to the greatest welding pressureand successive turns inwardly of such endmost turn being subject toprogressively less welding pressure as a result of the taper of saidterminal conductor pin whereby the degree of fusion of the'weldprogressively decreases inwardly of the coiled resistor member end froma maximum at said endmost turn to provide a graduated weld having bothmaximum mechanical strength and minimum electrical resistance.

3, In an electric heater, the combination comprising a resistor memberhaving a coiled end and a terminal conduotor pin secured to said coiledend to provide electrical continuity therebetween, one end of saidterminal conductor pin having axially spaced portions providingdifferent diameters for close fitting engagement within coiled resistormember ends each having a different inside diameter whereby the sameterminal conductor pin may be used with such various coiled resistormember ends, said coiled resistor member end being welded to thatterminal conductor pin portion which is in close fitting engagementtherewith to provide a permanent, low electrical resistance connectiontherebetween.

4. In an electric heater, the combination comprising a resistor memberhaving a coiled end and a terminal conductor pin secured to saidresistor member end to provide electrical continuity therebetween, oneend of said terminal conductor pin being tapered for close fittingengagement within various coiled resistor member ends each having adifferent inside diameter whereby the same terminal conductor pin may beused with such various coiled resistor member ends, said coiled resistormember end being welded to that terminal conductor pin portion which isin close fitting engagement therewith to provide a permanent, lowelectrical resistance connection therebetween.

5. In an electric heater, the combination comprising a resistor memberhaving a coiled end providing a plurality of turns in side by siderelation and a terminal conductor pin secured to said resistor memberend to provide electrical continuity therebetween, one end of saidterminal conductor pin having axially spaced portions providingdifferent diameters for closely fitting within various coiled resistormember ends each having a different inside diameter whereby the sameterminal conductor pin may be used with such various coiled resistormember ends, said coiled resistor member end being Welded to thatterminal conductor pin portion which is in close fitting engagementtherewith to provide a permanent, low electrical resistance connectiontherebetween and the degree of fusion of the weld progressivelydecreasing in a direction inwardly of said coiled resistor member endfrom a maximum at one of the latters endmost turns whereby successiveturns will be welded to said terminal conductor pin by means of agraduated weld having both maximum mechanical strength and minimumelectrical resistance.

6. In an electric heater, the combination comprising a resistor memberhaving a coiled end providing a plurality of turns in side by siderelation and a terminal conductor pin secured to said resistor memberend to provide electrical continuity therebetween, one end of saidterminal conductor pin being tapered for close fitting engagement withinvarious coiled resistor member ends each having a different insidediameter whereby the same terminal conductor pin may be used with suchvarious coiled resistor member ends, said coiled resistor member endbeing welded to that terminal conductor pin portion which is in closefitting engagement therewith to provide a permanent, low electricalresistance connection therebetween and the degree of fusion of the weldprogressively decreasing in a direction inwardly of said coiled resistormember end from a maximum at one of the latters endmost turns wherebysuccessive turns will be welded to said terminal conductor pin by meansof a graduated weld having both maximum mechanical strength and minimumelectrical resistance.

7. In an electric heater, the combination comprising a resistor memberhaving a coiled end providing a plurality of turns of uniform diameterin side by side relation and a terminal conductor pin secured to saidresistor member end to provide electrical continuity therebetween, oneend of said terminal conductor pin being tapered for close fittingengagement within various coiled resistor member ends each having auniform but different inside diameter whereby the same terminalconductor pin may be used with such various resistor member ends, saidcoiled resistor member end being welded to that terminal conductor pinportion which is in close fitting engagement therewith to provide apermanent, low electrical resistance connection therebetween and thedegree of fusion of the Weld progressively decreasing in a direct ioninwardly of said coiled resistor member end from a maximum at one of thelatters end most turns whereby successive turns will be welded to saidterminal conductor pin by means of a graduated Weld having both maximummechanical strength and minimum electrical resistance.

References Cited in the file of this patent UNITED STATES PATENTS2,055,849 Mucher Sept. 29, 1936 2,637,797 Schenk May 5, 1953 2,653,992Hill Sept. 29, 1953 Disclaimer 2,899,666.Leste1" D. Drugmamcl and JosephM COTZZy, Pittsburgh, Pa. TERMINAL PIN RESISTOR ASSEMBLY FOR ELECTRICHEATERS. Patent dated Aug. 11, 1959. Disclaimer filed Feb. 23, 1966, bythe assignee, Edwin L. Wz'egcmd Company. Hereby enters this disclaimerto claim 4 of said patent.

[Oficz'al Gazette May 31,1966.]

Disclaimer 2,899,666.Lestew D. Dmgmand and J 0861072, McOrZZy,Pittsburgh, Pa. TERMINAL PIN RESISTOR ASSEMBLY FOR ELECTRIC HEATERS.Patent dated Aug. 11, 1959. Disclaimer filed Feb. 23, 1966, by theassignee, Edwin L. Wiegami Company. Hereby enters this disclaimer toclaim 4 of said patent.

[Ofiioial Gazette May 31,1966]

